The marine (saltwater) and freshwater of many countries are increasingly impacted by the environmental and socioeconomic problem of harmful algal blooms (HABs). HABs are proliferations of marine and/or freshwater algae that can produce toxins or accumulate in sufficient numbers to alter ecosystems in detrimental ways. These blooms are often referred to as “red tides,” but it is now recognized that they may also be a variety of colors (e.g., green, yellow, brown, or even without visible color), depending on the type and number of organisms present. The majority of HAB species are phytoplankton, which are micro algae (microscopic, single-celled algae) or cyanobacteria that live suspended in water. This harmful algae also includes some micro algae that live attached to plants or other substrates as well as some species of macro algae (seaweeds). HABs are found in expanding numbers of locations and are also increasing in duration and severity. Additionally new HAB species are being identified that pose new threats to human and ecosystem health.
HAB deplete nutrients and oxygen, shade the deeper water areas, limit light-dependent processes, and release toxins that affect fish and shellfish, which are part of the human food chain. For water intakes HAB events place higher demands on the filtration systems, requiring not just more frequent cleaning, but also mitigation against toxin release and dispersion. In severe cases, HAB events force the shut-down of services to prevent irrecoverable damage to treatment systems. In addition, polysaccharide secretions of HAB bypass all stages of filtration except for the reverse osmosis (RO) membrane. Further, Transparent Exopolymer Particles (TEP) which are primarily hydrophilic polymeric substances that exist as gel networks or slimes and can split during passage through even ultra-fine (UF) membrane pores and thereafter reform back into such gel networks or slimes.
If moderate to large algae cells (greater than 15 to 20 microns in diameter) exceed 15,000 cells per mL of water, it is referred to as a bloom. For small microscopic cells (less than 1-5 microns) concentrations in excess of about 100,000 cells per mL are considered a bloom. The concentration of algal cells on the surface can vary during the day, and can be 20-50 times the ‘integrated’ density in calm conditions. However, impacts can result from lower densities, for example, a bloom of a toxic species in a shellfish harvesting area could pose a threat at densities as low as 5 cells per ml.
Current approaches to minimize the impact of HABs include:                1. Prevention, i.e., minimizing nutrient pollution or spreading of known HAB species to new locations;        2. Control, i.e., the direct reduction or containment of existing blooms, which can include mechanical, biological, chemical, or genetic approaches; and        3. Mitigation, i.e., monitoring, short-term prediction, and event response to minimize the impact of HAB on humans.        
The control approaches are limited by the need to keep the algae intact during the removal to prevent the release of excess toxins. Any chemical and/or biological approach should also be algae specific, since most algae present in any water body are beneficial to the environment and should not be eradicated with the harmful algae species. Examples for “mechanical removal” include the physical removal of macro algae or the application of clay as a flocculent to sediment out cells and their toxins from the water. The second approach leads to a deposition of a potentially toxic algae layer at the bottom of the water body, which may impact the living organisms there.
It may be desirable to remove such toxic algae in order to eliminate them as a source of poison for other marine life, such as, for example, shell fish. Doing so without rupturing the cells of the micro-organisms becomes increasingly critical so as to avoid the release of toxins or other harmful matter that may contaminate the ecosystem.
A particularly difficult aspect of such blooms is that they often extend off-shore (while at other times they do reach shorelines). Therefore, reaching the blooms when off-shore adds a further complicating factor.
It is therefore deemed desirable to provide systems (and/or devices) and processes to mitigate NABS and/or TEPs that exist off-shore, near-shore, or on-shore.